MG4 Reduction Gearbox Oil Leak

[stevegus]

Most diesels would deliver there torque in a gradual way where an EV can deliver it almost Instantaneously.
Les


I wish you luck with it my friend, and if it does work maybe you could start a supply chain from Scotland to Birmingham longbridge and we could all have one fitted in a couple of weeks and maybe put this thread to bed.
Les

Most Diesels produce max torque around 1500-1800 rpm. Pretty much from the get go. And if its on an old style automatic torque converter the take of torque will be multiplied.

 

[Noblapod]

I have a theory that the problem is temperature related. My car has the modified breather, fitted in November when I bought the car. It has been fine on local journeys but I noticed some oil on the undertray today just a few days after doing a long, fairly hard driven journey of 130 miles. If my theory is correct then we will be seeing more leaks as the ambient temperature increases in the spring and summer. Time will tell.
All the best...Chris.

 

[Ayoull]

I have a theory that the problem is temperature related. My car has the modified breather, fitted in November when I bought the car. It has been fine on local journeys but I noticed some oil on the undertray today just a few days after doing a long, fairly hard driven journey of 130 miles. If my theory is correct then we will be seeing more leaks as the ambient temperature increases in the spring and summer. Time will tell.
All the best...Chris.

When we fill transformers and switchgear at work with oil we have to adjust the volume based on ambient temperature at the time of filling.

I'd hope MG would do the same as 900ml at 0c will be a different volume at 15c

 

[Noblapod]

I have a theory that the oil leak is temperature related. My car has the modified breather fitted and it seems to be fine on local short journeys but I have just noticed some oil on the undertray just a few days after a long (130 mile) journey which was driven fairly hard. The drivetrain would have got much hotter on this journey than it would on short local trips. If I am right we will be seeing more leaks as the ambient temperature increases in spring and summer. Oil also gets thinner as it gets hotter but whether this would make a difference I have no idea.
Time will tell.
All the best...Chris.

don't know why this has double posted...sorry.

 

[Macadoodle]

Oil also gets thinner as it gets hotter but whether this would make a difference I have no idea.

More than likely has an effect. Also, synthetic oil tends to creep into every nook as many an owner of older cars found out when seals started to let by upon changing to synthetic back in the day.

I can't help thinking the design of this gearbox is fundamentally flawed re the positioning of the breather.
If they had side mounted it, it wouldn't be in direct line of fire from the considerable spray coming off the spinning gears.
Also wonder if positioning it above the motor output shaft was a mistake ? If they had put it above the diff ring gear on the other end of the box, it would be above a cog spinning around 8 times slower

 

[Cocijo]

From what I can see ALL MG4 cars will leak oil. It’s not if but when.
The modified breather may bring some improvement but this leak will not just occur on some cars. If your car hasn’t leaked yet - it will, once the conditions are met.
MG should be fitting the best solution to all cars but they are not.
Some owners will not notice the leak even though it is present.
Others might rarely meet the conditions for it to leak but it will happen eventually to all cars unless fixed satisfactorily.

 

[siteguru]

It is certainly a factor of speed and temperature. As the temperature increases (both ambient, and internal based on speed) then the oil will get thinner (less viscous), but also the pressure inside the casing will increase in proportion to speed. (That's the point of the breather - to allow excess air pressure to escape). Based on its position relative to the gear cogs then the original breather is bound to fail - everyone will likely experience this at some point.

The modified breather should work (the bends should remove the kinetic energy of the oil flung from the gears) but it's apparent that it doesn't work for everyone - it doesn't for me.

So let's see what MG come up with next.

 

[WigglePig]

<snip>

The modified breather should work (the bends should remove the kinetic energy of the oil flung from the gears) but it's apparent that it doesn't work for everyone - it doesn't for me.

So let's see what MG come up with next.

What I suspect is happening here, based on other experience with mechanical systems is that the oil fling directly onto/into the breather leads to small "plugs" of oil sitting in the channel which are then pushed out by the expanding air as the gearbox heats up. The longer breather would increase the amount of time/airflow necessary along with increasing the amount of heating needed to push oil out but wouldn't stop it from happening. It only requires a relatively small amount of oil to escape, a drip an hour say, to make quite the mess after a while and left for a few hundred miles this can all add up.
Having seen this in machinery and automotive gearboxes before (F23 on the Vauxhall VX220 is a case in point) there are a fair number of alternative arrangements around to avoid dropping oil. If you google them then these items (especially the VX220 one as it was quite an issue) pop up really quickly. Basically these usually consist of some sort of bottle, bottom-fed, so the oil can collect there as it is pushed up the breather and drain back under gravity, sort of like a much fatter version of the "fix" part being fitted by dealers. If one of these overflows then there is something very bad going on!

This is the one currently available for the F23 box, although you'd only need one hose so could happily plug off the second input.

EDIT: Having done this from memory I decided to have a Google about gearbox oil breather problems and they are much, much more common on vehicles than you might have thought...hundreds and hundreds of pages about it!

 

[Macadoodle]

That looks like a solution, might cost more than MG's £2.99 'goodwill' budget unfortunately.
You can understand how the change in air volume involved in say a 6 speed manual tranny will be significant, but these little reduction boxes are tiny in comparison, how could they get it so wrong ?

I always thought they fitted prototypes with a Perspex casing on a test rig to actually see in real time how the fluid dynamics are working in regards to lubrication and oil distribution to gears and bearings.
You would also think that a simple baffle protecting the 4mm hole in the breather inside the case would cut the chances of leaking dramatically, makes you wonder if there's one in there at all.

 

[Cocijo]

I wonder if the fact that it is at the rear of the car has affected this In any way?

 

[siteguru]

What's your thought process to think that?

 

[WigglePig]

<snip>
You would also think that a simple baffle protecting the 4mm hole in the breather inside the case would cut the chances of leaking dramatically, makes you wonder if there's one in there at all.

That there is the issue, I'm sure. Not having seen inside one of these 'boxes (are there any photos around?) I'm not sure if there would be enough space for it in this case but stopping the splashing on the breather would be a very good start.

 

[Cocijo]

I’m thinking that this is the first rear wheel drive set up by MG. There has been no oil issues with their front wheel drive cars as far as I can see. Perhaps the transfer box runs cooler on FWD set up? Or perhaps just the designing the RWD transfer box has built in design flaws?

 

[WigglePig]

That looks like a solution, might cost more than MG's £2.99 'goodwill' budget unfortunately.
You can understand how the change in air volume involved in say a 6 speed manual tranny will be significant, but these little reduction boxes are tiny in comparison, how could they get it so wrong ?
<snip>

Indeed, although all it would really need is an expansion bottle type arrangement at the top, perhaps with the breather valve mounted on top of that, so that wouldn't be expensive at all.

Perhaps something like this at £12 with the original ball-valve breather cap fitted into the lid?

As a note, it wouldn’t need to be anything like this big as the amount of oil at any one time is small, it just makes a mess over time.

 

[Cocijo]

That there is the issue, I'm sure. Not having seen inside one of these 'boxes (are there any photos around?) I'm not sure if there would be enough space for it in this case but stopping the splashing on the breather would be a very good start.

Yes. They are not that large. Many ‘axles’ and transfer boxes have internal baffles to deflect oil.

 

[Macadoodle]

I’m thinking that this is the first rear wheel drive set up by MG. There has been no oil issues with their front wheel drive cars as far as I can see. Perhaps the transfer box runs cooler on FWD set up? Or perhaps just the designing the RWD transfer box has built in design flaws?

There's certainly limited space above the box but other RWD cars seem to manage to be leak free.
Well, I've taken delivery of 50cm oil resistant hose today, so if the storm conditions subside over the weekend I might have a go at designing my own solution.
My other thought is using a length of 10mm clear tubing instead, and setting up a go pro pointing at the breather outlet to see just what goes on
Not sure if I could mount it reliably though, be a shame if it fell off and got crushed by a bus

 

[Cocijo]

Indeed, although all it would really need is an expansion bottle type arrangement at the top, perhaps with the breather valve mounted on top of that, so that wouldn't be expensive at all.

Perhaps something like this at £12 with the original ball-valve breather cap fitted into the lid?

I’m far from an expert on this, but is there not a concern that if the actual overall design is flawed that under load and heat there may be insufficient lubrication due to, for example, oil being pushed out into an ‘overfLow’ type arrangement. There must be a design test that retains sufficient lubricant under operating conditions regardless of the venting system and also defines the required oil capacity and level. In this case there is only around 400ml of oil to start with?

 

[Deleted member 10041]

I’m far from an expert on this, but is there not a concern that if the actual overall design is flawed that under load and heat there may be insufficient lubrication due to, for example, oil being pushed out into an ‘overfLow’ type arrangement. There must be a design test that retains sufficient lubricant under operating conditions regardless of the venting system and also defines the required oil capacity and level. In this case there is only around 400ml of oil to start with?

The big red flag for me was the colour of macadoodles oil after just a few weeks

 

[Cocijo]

Yes. It should not be like that. I’ve drained axles after quite a bit of mileage and the oil stays relatively clean.

 

[WigglePig]

I’m far from an expert on this, but is there not a concern that if the actual overall design is flawed that under load and heat there may be insufficient lubrication due to, for example, oil being pushed out into an ‘overfLow’ type arrangement. There must be a design test that retains sufficient lubricant under operating conditions regardless of the venting system and also defines the required oil capacity and level. In this case there is only around 400ml of oil to start with?

It's more that it slowly, slowly ejects the oil meaning you may end up with insufficient in the 'box. With a proper breather catch arrangement then it will always drain back into the 'box so that shouldn't become a problem. All breathers will lose some oil to some extent, it's just that this one, being right in the line-of-fling, seems to allow rather more to exit. The longer breather pipe, as fitted as a fix, will make it better but won't necessarily completely stop the issue which appears to be related to the location of the breather.